U.S. Patent Application Publication No. 2007/0121970 discloses an electrostatic transducer whose driving circuit uses a class-D amplifier, and the output of the class-D amplifier is necessarily coupled with a low-pass filter to eliminate the switching carrier components included in the output signal of the class-D amplifier. However, the low-pass filter unavoidably increases the volume and cost of the physical device. While exactly helping to reduce the volume and cost of a physical device, a filterless class-D amplifier is only applicable to inductive transducers. On the other hand, the conventional electrostatic transducer needs a very high direct current (DC) bias voltage, and thus requires a power supply circuit capable of providing the high DC voltage, thereby causing the resultant physical device bulky and costly. U.S. Patent Application Publication No. 2009/0016551 discloses an electrostatic transducer which is needless of DC bias voltage and thus is useful in applications to decrease the volume and cost of a physical device.